This invention relates to a class-D amplifier suited for a power amplifier of an audio apparatus, etc.
A class-D amplifier is an amplifier for generating a pulse train with the pulse width or the pulse time density demodulated in response to an input signal and driving a load according to the pulse train. This class-D amplifier is often used as a power amplifier for driving loudspeakers in an audio apparatus, etc. Patent Documents 1 to 3 disclose each a class-D amplifier including a differential integrator for integrating differences of an input signal and a feedback signal output from the class-D amplifier, and a pulse width modulation circuit for generating a pulse having the pulse width corresponding to the level of an integration value signal output from the differential integrator. The class-D amplifier drives a load based on an output pulse of the pulse width modulation circuit.    [Patent document 1] JP-A-2007-124624    [Patent document 2] JP-A-2007-124625    [Patent document 3] JP-A-2006-262104
By the way, the class-D amplifier may be required to have a power limit control function of limiting output power within predetermined desired range for the volume control, etc., of a loudspeaker as a load depending on the intended purposes of the class-D amplifier. In a related class-D amplifier, a clamp circuit is provided in an input path of an input signal to a differential integrator for clamping the input signal so that the input signal input to the differential integrator does not exceed the desired level, thereby implementing the power limit control function. However, in such as configuration, the input signal input to the differential integrator is clamped by the clamp circuit, and thus there is a problem of occurrence of a large waveform distortion in the output signal of the class-D amplifier.